In the manufacture of air impellers and other rotary fluid moving devices of molded plastic construction, hubs of metallic construction are frequently employed to provide a higher degree of structural integrity in the hub-shaft connection, e.g., as in better retention of set screws with stronger and more durable metallic threads. When metal hubs are inserted into the mold which produces the plastic part and thus molded in place in the air impeller or other device, the resulting product may be satisfactory with certain plastics and for certain applications but in other instances severe problems are encountered. More particularly, plastics with high shrinkage rates may result in a desirable end product but undesirably high levels of stress may occur in the plastic adjacent a metal hub inserted in the molding process. Further, and in the case of any plastic air impeller or like device provided with a metal hub during molding, there is an economic disadvantage. That is, the cycle time for the molding operation is increased by the time consumed in inserting the metal hub into the plastic mold and a resulting inefficiency and an increase in manufacturing costs is encountered.